levelclamp: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/lib64/piglit/bin/levelclamp - from package: piglit

You may install the required package with command yum install {package}

Error in other languages:
levelclamp: bevel nie gevind nie
levelclamp: comandă negăsită
levelclamp: comando não encontrado
levelclamp: commande introuvable
levelclamp: command not found
levelclamp: käsku ei ole
levelclamp: không tìm thấy lệnh
levelclamp: komanda nerasta
levelclamp: Kommando nicht gefunden.
levelclamp: kommandot finns inte
levelclamp: komut yok
levelclamp: nie znaleziono polecenia
levelclamp: níor aimsíodh an t-ordú
levelclamp: no se encontró la orden
levelclamp: no s'ha trobat l'ordre
levelclamp: opdracht niet gevonden
levelclamp: parancs nem található
levelclamp: perintah tidak ditemukan
levelclamp: príkaz nenájdený
levelclamp: příkaz nenalezen
levelclamp: команда не найдена
levelclamp: командата не е открита
levelclamp: 命令找不到
levelclamp: コマンドが見つかりません